The invention relates to a process and agents for controlling the swelling of clays especially in the presence of sea-water, more particularly within the scope of the use of said clays for the constitution of drilling fluids, called in the art "drilling muds".
It relates also to clay-based muds obtained by the use of the abovesaid process and agents and constituting novel industrial products.
The use of clays for the constitution of drilling fluids which are used especially for carrying to the surface the cuttings released by the action of the drilling tool, is well-known.
These fluids are then freed from the cuttings that they have entrained, then they are re-circulated after having been "replenished" with those of their constituents which are found to be exhausted.
Clays, by their well known swelling in the presence of water, confer on these fluids a consistency of "muds", whence the expression "drilling muds", of which the viscosity must be such that the cuttings are correctly removed and are deposited as little as possible by sedimentation on standing, without however offering prohibitive resistance to the rotation of the constituent elements of the drilling tool.
Moreover, the consistency of the mud must be such that what is called "filtration" of the water which enters into its constitution, is avoided, that is to say the "migration" of this water into the geological strata traversed, which migration is manifested by an imbalance in the composition of the mud and by the deposition of a "cake" on the walls of the well bore capable of resulting, once it has reached a sufficient thickness, inconsiderable mechanical friction.
Finally, when the drill passes through geological layers based particularly on clay, the drilling fluid or mud must not cause the swelling of this clay since such swelling can result in the sticking of the clay to the drill string to the extent of preventing the continuation of drilling; the contact of the mud and of the wall must not cause the shrinking of the clay constituting the wall either, which would result in the formation of cavities, cavings and settlements in the well bore and, here again, would stop the drilling. Finally, the mud must not be the cause of a slow change in the geological layer based on clay which would create pressures strong enough to destroy, for example, the infrastructures of a well under exploitation.
The behavior of clays, which is different when they are contacted with soft water or salt water, particularly sea-water, is well known; soft water is especially used for the constitution of drilling fluids in the case of drillings on land--but then these fluids may possibly be placed in contact with salt water present in certain geological layers through the drilling passes--whereas salt water, that is to say, in practice, sea-water, is used for the constitution of muds in sea drillings of the "offshore" type.
The principal type of clay used for the constitution of drilling fluids is that of the bentonite family.
The latter gives satisfaction as long as the water used is soft water.
Their drawback is, on the other hand, not swelling in the presence of sea-water.
For that reason, when drilling fluids are constituted with sea-water, another type of clay, i.e. attapulgite, is used which in fact swells in the presence of sea-water, but whose properties are not so good, especially as regards reduction of the filtrate, that is to say the loss of water by filtration, which must then be compensated by additives such as modified starches.
Once the technician skilled in the art has selected the clay, particularly according to the place--on ground or at sea--of the drilling, he must select a certain number of additives which are well known and on all of which it is hence unnecessary to dwell here; by means of these additives, he confers on the final drilling fluid the above-mentioned properties of viscosity, filterability, inertia with respect to the clay of clay-based geological layers traversed during the drilling and the like.
To render the mud inert with respect to the clay of the clay-based geological layers traversed during drilling, the technician skilled in the art conventionally uses various products, particularly sodium chloride, gypsum, lime, calcium chloride and the like; U.S. Pat. No. 3,086,937 proposes to improve the results recorded with these products by resorting to tetra(hydroxyalkyl)alkylene diamines; in other words, this U.S. patent describes drilling fluids containing said diamines, these fluids being, conventionally, based on attapulgite when the water used for their constitution is sea-water, based on bentonite when the water used is soft water.
This patent hence does not provide a solution to the problem posed by the impossibility of using bentonites when the water taken for the constitution of the drilling fluid is sea-water.
Now, if only from a practical point of view, the user would like to be able to use bentonites as well as attapulgite for ocean drillings.
This is the problem that Applicants have attempted to solve.